Methods that exhibit the features of the present invention are known from the prior art. In this case, the fuel pump is a high pressure pump, which is located downstream of an electrically regulated low pressure pump. Thus, the fuel is conveyed first from the low pressure pump to an inlet of the fuel pump. At the same time, the pressure of the fuel is adjusted in a controlling and/or regulating manner to a predetermined desired value (typically, in a magnitude of 5 to 6 bar). For this purpose there is, for example, a low pressure sensor, which is arranged on the inlet side of the fuel pump. Then the fuel is conveyed from the fuel pump into the pressure accumulator, the so-called fuel high pressure rail. This pressure accumulator is connected to injection valves by means of which the fuel can be introduced into the internal combustion engine. In more precise terms, the fuel can be introduced into a combustion chamber of at least one cylinder. Thus, the injection valve controls or rather regulates the amount of fuel that is introduced into the combustion chamber. At the same time, this amount of fuel is adjusted to the amount of air that is in the cylinder. In order to adjust the amount of fuel, the invention provides that the opening duration of the injection valves is adjusted to a defined injection time.
The pressure in the pressure accumulator is the decisive factor that influences the combustion in the internal combustion engine or rather in the cylinder. As a function of the operating mode of the internal combustion engine, the pressure in the pressure accumulator can be suitably adjusted with respect to the consumption, emission, power output, and smooth running of the internal combustion engine. For this purpose, the pressure is adjusted in a controlling and/or regulating manner to different desired values as a function of a number of parameters, such as the load and rotational speed. In this case, the resulting lowest pressure is, for example, in a magnitude ranging from approximately 25 to 35 bar. The resulting maximum pressure depends on the type of injection valves or rather the drive unit that is used. In order to measure the pressure prevailing momentarily in the pressure accumulator, there is a pressure sensor. The sensor signals of the pressure sensor or rather the pressure measured with the pressure sensor is also used to calculate the injection time that is required to introduce the desired amount of fuel into the internal combustion engine, because the injection time depends predominantly on the pressure in the pressure accumulator. For this purpose, the pump control unit of the fuel pump is suitably adjusted. To this end, there is a pilot control unit that in the case of a drive unit leads to the adjustment of the desired pressure in the pressure accumulator without any disturbances. In order to compensate for the influence of disturbances (in particular, caused by defects and/or malfunctions of the drive unit), the pump control unit is provided with a regulator. Potential defects of the drive unit include, for example, a malfunction of the fuel pump (in which case, either a too high or a too low amount of fuel is introduced into the pressure accumulator), a pressure loss, or a malfunction of the pressure sensor, which on the basis thereof delivers an incorrect sensor signal. Such defects and/or malfunctions have an extremely adverse effect on the dynamic behavior of the internal combustion engine and additionally on the emissions, both of which can be discerned by the person using the drive unit.
Therefore, monitoring the internal combustion engine with respect to such malfunctions is logical and to some extent even prescribed by law. In the case of the aforementioned malfunctions, a disturbance acts on the whole system of the internal combustion engine and the drive unit, a circumstance that results in the pump control unit or rather the regulator of the pump control unit having to make readjustments, because the pilot control, which is matched to a system without any disturbances, no longer results in an adjustment of the desired pressure in the pressure accumulator. In the case of a fuel pump which pumps too little fuel and/or in the case of a pressure loss, the pump control unit adjusts the fuel pump in such a way that the amount of fuel delivered by this pump increases. In the case of a fuel pump which delivers an amount of fuel that is too much, the pump control unit adjusts the fuel pump in such a way that the amount of fuel that is delivered is decreased.
Furthermore, the internal combustion engine is provided with a lambda function unit, which monitors the composition of the fuel-air mixture that is introduced into the internal combustion engine. Thus, this lambda function unit can check whether the composition that is actually on hand corresponds to a desired and/or adjusted composition. Thus, both the pump control unit and the lambda function unit have output variables that can be used to determine the malfunction of the internal combustion engine. In this respect, the output variable of the pump control unit can establish whether an adjustment of the delivery capacity of the fuel pump is necessary, based on the value set by the pilot control unit, in order to obtain the desired pressure in the pressure accumulator. At the same time, the lambda function unit can determine whether the current composition deviates from the adjusted composition of the fuel-air mixture. In this case, the lambda function unit establishes primarily whether the amount of fuel that has been introduced into the internal combustion engine has to be increased or decreased.
As soon as the output variables of the pump control unit and/or the lambda function unit exhibit a deviation from a desired behavior of the drive unit, there is the possibility of a malfunction of the internal combustion engine. However, there may be cases in which it may not be possible to establish which component of the internal combustion engine is exhibiting a malfunction, that is, for example, whether the fuel pump or the pressure sensor is defective or whether there is a pressure loss. This is especially the case when several structural parts or rather components of the drive unit are defective and/or exhibit a malfunction at the same time.
Therefore, the object of the invention is to provide a method that does not exhibit this drawback, but rather makes it possible to determine with a higher degree of accuracy the component that exhibits a malfunction.